Metal disintegrators are used to remove broken taps, drill bits, and the like from pieces of bulk metal in which they have broken off and are embedded. The metal disintegrators operate by charging a hollow, tubular electrode to, for example, approximately 28 volts dc with the electrode positioned coaxial with and just above the embedded metal. The electrode is then vibrated longitudinally so as to repeatedly make and break contact with the embedded metal. The voltage potential with respect to the embedded metal varies which causes current to flow during contact, which in turn, causes localized heating to occur. The continued vibration causes a break in contact which causes an arc to flow from the electrode to the embedded metal, with substantial increases in temperature. Generally, the rate of vibration will be approximately 50 or 60 Hz. A stream of liquid coolant, such as water having a small amount of oil intermixed therewith, is propelled under pressure through a longitudinal passage in the electrode and onto the embedded metal. The liquid coolant creates thermal shock, causing fractures and metal disintegration. As the metal disintegrates and is converted into a powder, the liquid washes away the disintegrated powdered metal.
The hollow, tubular electrodes used in metal disintegrators are typically made from copper, graphite, tungsten, brass, molybdenum or alloys thereof. The electrodes generally are available in lengths of approximately 3 inches to 36 inches, and outer diameters of approximately 0.040 inches to 0.312 inches. The spark or discharge end of the electrode is consumed during the disintegration process. The consumable electrode may be attached at one end to the metal disintegrator by a quill or similar device extending longitudinally from the disintegrator head.
Selection of the electrode material and size depends upon the nature of the workpiece. It may be necessary for the electrode to be inserted into a narrow opening, or offset from the quill in order to reach the embedded material. Larger diameter electrodes, diameters greater than 0.312 up to 1.000 inches, may be necessary for special work. Special conditions, such as the need for a large diameter electrode and/or an offset workpiece, require the metal disintegrator operator to custom build, or to stock, specialized quills and/or connecting devices.
Smaller diameter electrodes, molybdenum electrodes for example, are delicate and easily broken if accidentally bumped or struck against the workpiece. The vibration produced by the disintegration process inherently contributes to the possibility of contact between the electrode and portions of either the workpiece or any objects found in the immediate environment thereby increasing the possibility of breakage of the electrode. Additionally, vibrations create "whip" at the tip of longer electrodes and thereby increase the possibility of contact between the electrode tip and the workpiece.
A significant problem with the electrodes of the prior art is that of bending, splitting and breakage. Certain electrodes, such as molybdenum electrodes, may be small in diameter and very expensive. The quill typically secures only one end of the electrode and the remaining length is unprotected during operation. Breakage is common and the shorter, broken-off lengths are frequently unusable for the next workpiece. Additionally, breakage interrupts the disintegration process while the operator changes electrodes. The proper length of the desired electrode may be unavailable. Metal disintegrator operators typically end up with a box of expensive, unusable electrode pieces and custom-constructed offset electrodes for special conditions.
Attempts have been made to join shorter electrode lengths to reduce waste in the industry. Solder has been used and glues, such as epoxy, have been tried to join smaller molybdenum electrodes. Solder and glue are less than successful and the result is often a weakened electrode. It is also time consuming to solder or glue electrode pieces together and such repairs may also result in an acid or resin residue which, if contact is made with a highly ground workpiece, may produce oxidation and resultant damage to the workpiece.
Offset workpieces have required the custom construction of electrodes using solder or epoxy, a process that is time consuming and expensive.
As can be seen from the above discussion of the prior art, an unsolved need exists in the field of metal disintegration for a universal fitting for connecting electrodes of short lengths and of any diameter, for protecting the electrodes, and for permitting electrode lengths to be easily joined together for both routine and offset work.